The Supreme Court made a decision on President Obama's health care law, but did not end the debate. Voters in battleground states remain polarized about that law. There are signs, though, that the gap between opponents and supporters has become a little smaller. This is the first NPR poll of the 2012 general election season, and we have more, this morning, from NPR's Mara Liasson reports.

MARA LIASSON, BYLINE: Our poll of 1,000 likely voters was conducted by NPR's bipartisan team: veteran Stan Greenberg of Democracy Corps and a new Republican pollster, Whit Ayres of Resurgent Republic. Democracy Corps conducts public polling for Democrats. Resurgent Republic does the same for Republicans. Our poll showed Presidents Obama's approval rating nationally to be just under 50 percent, an important threshold for incumbents. But Mr. Obama has a small two point lead over Mitt Romney in the horse race. Democrat Stan Greenberg thinks he knows why.

STAN GREENBERG: This poll has the Democrats with a seven point advantage on party identification. The image of the Republican Party right now is not great. There are more Democrats than Republicans in the electorate. And so the Democrats have a slight edge in this election.

LIASSON: But that doesn't mean that seven percent more Democrats will turnout in the fall, says our Republican pollster Whit Ayres.

WHIT AYERS: Because Republicans are significantly more energized than are Democrats and independents. Eighty-five percent of Republicans say they're absolutely certain to vote, compared to 75 percent of independents and 76 percent of Democrats. So the Republican enthusiasm advantage is going to narrow that partisan gap in ultimate turnout.

AYERS: The battleground states are those where the vast majority of spending occurs for the presidential campaigns. Those are the voters who are actually hearing the messages, watching the ads, and being - one presumes - most tuned in to the presidential election.

LIASSON: In the battleground, the race is tighter than nationally. It's dead even, 46 to 46. And the number of undecided voters there is tiny - just three percent. And when we asked likely voters in the battleground about the health care law we found that while they were evenly split on the Supreme Court decision upholding the law, the law itself was still underwater. Ayres and Greenberg each had their own read of our results.

AYERS: Even after the Supreme Court decision, Republicans oppose it at a higher - level 87to eight - than democrats support it - 77 to13. A majority of independents oppose it - 50 to 37, a double digit opposition margin - as do battleground state voters - 52-39. The health care reform law is still an albatross around the president's reelection campaign.

GREENBERG: No, no, no, no, no. I mean, this poll in fact undermines the conventional wisdom, which has been health care hangs over the Democrats. What we have here, is almost an even split on health care. It's lost much of its intensity.

LIASSON: Greenberg is pointing to what the polls showed when he and Ayes tested the best arguments Democrats and Republicans could offer about the law. Then the gap narrowed. When given a choice between repealing Obamacare - the GOP battle cry - and moving forward to make improvements in the law, the Democratic argument actually won battleground voters 53 to 44 percent. Big majorities - 58 percent of battleground voters - said the Supreme Court's decision would have no effect on their view of the law.

Voters like Arlene Harper, a retired nurse from Kentwood, Michigan - an independent - who says she's leaning to Romney.

ARLENE HARPER: To me that's pushing us closer and closer to socialized medicine. But no, I do not like this business of insurance, forcing people to get that.

LIASSON: Dan Bonga, a retired teacher from Wilkinsburg, Pennsylvania and a supporter of the law, says the Supreme Court's decision did affect his thinking about the presidential election.

DAN BONGA: Oh, it made me even stronger for Obama. And they worry about socialized medicine. We already have socialized medicine. You know, you're some crazy person, you get stabbed on the street, you go to the hospital, they take care of you and we pay for it.

LIASSON: Ayres and Greenberg agree that our poll shows there is an advantage for both candidates on health care, if they keep talking about the law. And they are.

MITT ROMNEY: There are a lot of things that need to be done to improve health care, but Obamacare is not the answer. We got to replace it. Get rid of it.

(SOUNDBITE OF CHEERING)

PRESIDENT BARACK OBAMA: So when you hear about the Affordable Care Act - Obamacare...

(APPLAUSE)

OBAMA: ...and I don't mind the name, because I really do care. That's why we passed it.